Question

the focal length of a concave lens is 2.5 cm if its magnification is ⅕ for an object placed at 10 cm then what will be the magnification for object placed at 3.5 cm​

Answer 1

Explanation:

Given:u=−10cm f=20cm (convex lens)

To find: v and image's nature.

Solution: From lens formula

v

1

−

u

1

=

f

1

v

1

+

10

1

=

20

1

v

1

=

20

−1

v=−20cm

And magnification =

u

v

=2

Hence image formed is virtual, erect and magnified two times.